1. Field of the Invention
The present invention relates to a direct liquid feed type double-head writing instrument including each nib on both ends. In the present invention, “anterior or front” denotes a side of a first nib in a first ink tank and also the “anterior or front” denotes a second nib in a second ink tank, while “posterior or rear” denotes a side of the first ink reservoir in the first ink tank and also the “posterior or rear” denotes a side of the second ink reservoir in the second ink tank.
2. Description of the Related Art
This type double-head writing instrument discloses, for example, in Japanese Patent Unexamined Publication JP-A-2002-36786 as a writing instrument having a direct liquid feed-structured nib unit consisting of a nib, nib holder and ink tank detachably attached at both ends of a barrel. The JP-A-2002-36786 also discloses the double-head writing instrument having a nib, a cover plate, a clip and a color-specific band are colored in the same color as ink filled into an ink tank. At the same time, ink tanks, nib covers and caps are formed by transparent synthetic resins.
In the writing instrument of the JP-A-2002-36786, each of the ink in two ink housing parts is visually confirmed to be separated back and forth. In the writing instrument of the JP-A-2002-36786, particularly, in a case where a large amount of air exists in the ink housing part, when either nib is pointed downward, the distance between each of the ink in the ink housing parts becomes large, whereby this may lead to a reduction in aesthetic appeal. Further, where the writing instrument is contained and displayed in a pen stand or the like, ink color of the upper nib exposed out of the pen stand may be visually confirmed, however, ink color of the lower nib contained inside the pen stand cannot be visually confirmed. Accordingly, users may have inconvenience in this matter.
In addition, the writing instrument of the JP-A-2002-36786 is structured so that another member (color-indicating members) such as a clip or color-specific band of the same color with ink is attached to the cap in order to distinguish ink from the outside. Therefore, the writing instrument becomes larger in the number of parts and higher in production cost. Further, since the writing instrument of the JP-A-2002-36786 is structured so as for each cap to indicate the ink color, the cap must be attached only on the nib of the same color with the ink concerned. When the cap is attached by mistake on the opposite nib of a different color, a user may be confused in recognizing the color of the ink.
In addition, in the writing instrument of the JP-A-2002-36786, the bottom surface of the ink housing part in the ink tank is vertical to the axial direction. Thus, when the ink is filled into the ink housing part of the ink tank, the ink filling from a filling nozzle collides with the bottom surface of the ink housing part, and the ink may splatter outside. In particular, since in the case of a double-head writing instrument, a distance between the opening of the ink tank and the bottom surface is designed to be relatively short in the axial direction, ink is more likely to splatter out as described above.
Further, in the double-head writing instrument of the JP-A-2002-36786, no consideration is given to a relationship between a rear end of the guiding core projected from a rear end of the ink-retaining member and a ink level. Where the writing instrument is kept for a long time, with the nib pointed upward, the ink remaining inside the nib may drop back, or a capillary clearance inside the guiding core may clog due to dried ink. In this instance, there is the possibility of the occurrence of poor ink flow such as an inability to write or blurred writing at the nib which was kept pointed upward. In the conventional double-head writing instrument, in the case of a direct liquid type with nibs on the both sides having ink remaining members, when the writing instrument is stored in the upright position, either nib is inevitably pointed upward, and the above-mentioned nib pointed upward may often have an ink flow failure after a long-term storage of a nib pointed upward state. Further, in a double-head writing instrument, in the case of a direct liquid feed type with a nib on the one end having an ink remaining member, when the writing instrument is stored in the upright position for a long time, sufficient attention should be given so that the direct liquid feed nib is not pointed upward in order to avoid an ink flow failure.
Where the double-head writing instrument of the JP-A-2002-36786 with a small quantity of ink remaining in the ink reservoir is used for writing in a horizontal state or in a state where the nib is pointed diagonally upward, it may result in an insufficient contact between the guiding core and the ink inside the ink reservoir, thereby causing an ink flow failure such as an inability to write or blurred writing.
Where a partition is extendedly provided in the axial direction, a mold core pin for forming the partition may be bent to the inner radial direction due to resin pressure during formation of the barrel thereby resulting in holes in the partition or occurrence of a sink on the outer surface of the side wall of the barrel or the inner surface of the barrel which is connected with the partition. In particular, a sink on an outer surface of the wall of the barrel may cause a printing failure when decorative printing is applied on the outer surface of the barrel.